This invention relates generally to processing of radar data, and more specifically, to methods and systems for piecewise curve fitting of radar altimeter range gate data.
The proper navigation of an aircraft in all phases of its flight is based to a large extent upon the ability to determine the terrain and position over which the aircraft is passing. In this regard, instrumentation, such as radar systems, and altimeters in combination with the use of accurate electronic terrain maps, which provide the height of objects on a map, aid in the flight path of the aircraft. Electronic terrain maps are well known and are presently used to assist in the navigation of aircraft.
Pulse radar altimeters demonstrate superior altitude accuracy due to their inherent leading edge return signal tracking capability. The pulse radar altimeter transmits a pulse of radio frequency (RF) energy, and a return echo is received and tracked using a tracking system. The interval of time between signal bursts of a radar system is called the pulse repetition interval (PRI). The frequency of bursts is called the pulse repetition frequency (PRF) and is the reciprocal of PRI.
To scan a particular area with the radar altimeter, range gates are utilized within the radar altimeter to partition the swath created by a Doppler filter within the altimeter. A range gate is typically set in time, the time being the expected time for a transmitted signal to travel to the ground, reflect, and travel back to a receiving antenna. The range gate is set to allow, for example, the main lobe of the reflected return signal to be processed while rejecting harmonics of the return signal and radar returns reflected from objects other than the ground. To scan a certain swath, many radar range gates operate in parallel. With the range to each partitioned area determined, a record is generated representing the contour of the terrain below the flight path. Electronic maps are used with the contour recording to determine the aircraft's position on the electronic map. Such systems are extremely complex with all the components involved as well as the number of multiple range gates that are required to cover a terrain area. As a result, the computations required for such a system are very extensive.